1. Field of the Invention
This invention relates to a novel amino acid silicon polymer with good adhesion to the keratin layer of the skin, a method for preparing the amino acid silicon polymer, cosmetic particles surface-treated with the amino acid silicon polymer, and color cosmetic composition containing the cosmetic particles.
2. Background of the Related Art
Color cosmetics are generally used to hide defects of the skin such as freckles and have a fresh and fair complexion. There is a tendency to take the thick cosmetics on the face in order to hide the defects and have a desired complexion. In such a case, a thick make-up layer closes up the skin pores and thereby causes troubles to the skin. It is thus considered that a desirable color cosmetic can be applied to the face very thin and offer an excellent cosmetic effect without troubling the skin. That is, such a good color cosmetic can hide defects of the skin and provide a fair complexion.
Conventionally, examples of cosmetic particles used in color cosmetics include extender pigments such as talc, sericite, mica and kaoline, inorganic coloring pigments such as titanium dioxide, zinc oxide, Prussian blue, deep blue and ferric oxide, and nylon, polyethylene, cellulose or organic tar-based pigments. However, these cosmetic particles come undone off the skin because of weak adhesion to the skin and are easily removed with sweat or water due to low water resistance. The cosmetic particles also have low oil resistance and tend to aggregate with sweat to form a thick cosmetic layer, thereby closing up the skin pores and impairing skin suffocation.
In order to improve such disadvantages of the conventional cosmetic particles, i.e., inferior skin adherence, durability, water resistance and oil resistance, there are generally added a moisturizing agent such as glycerin, sorbitol, propylene glycol and 1,3-butylene glycol, and an oil component such as liquid paraffin, camellia oil, olive oil, evening primrose oil, castor oil, octyl dodecanol and octyl palmitate. However, an excess of the moisturizing agent and the oil component makes the color cosmetics oily and greasy and a lack of them causes the cosmetic particles to come undone off the skin and incurs the dust raising effect.
Accordingly, to overcome the above problems, the articles are surface-treated in an appropriate method. That is, the particles are coated with a moisturizing agent or an oil component or treated with fatty acids, metallic soap of fatty acids, fluorides, silicon, amino acids, or the like. These methods for surface-treating the particles are, however, disadvantageous as follows:
(1) In a method of coating particles with a moisturizing agent, the cosmetic particles thus prepared can be enhanced in the moisture content but easily removed with sweat or water due to low water resistance. Therefore, this method is inapplicable to cosmetics for the summer.
(2) In a method of coating particles with an oil component or a fatty acid, the cosmetic particles thus prepared can be enhanced in water resistance, thereby generating intense repulsion to water, but easily thickened due to such a low oil resistance as to aggregate the particles with the oil component of the sweat. Such particles applied to the skin form a thick make-up layer, thus closing up the skin pores and impairing skin suffocation, and deteriorate durability of the cosmetic as to cause the cosmetic powder to come undone off the skin and aggregate after an elapse of long time.
(3) In a method of treating particles with fluorides, the cosmetic particles thus prepared can have good water resistance and oil resistance. Yet, such cosmetic particles are inferior in particle-skin adhesion as well as particle-particle adhesion. Hence, the cosmetic particles applied to the face tend to come undone off the skin and cause the dust raising effect.
(4) In a method of surface-treating particles with silicon, the cosmetic particles thus prepared are excellent in water resistance, dispersion and usability but inferior in the affinity to bio-components constituting the skin, thereby causing extraneousness. Further, the cosmetic layer is easy to become undone off the skin and the pigment particles easily aggregate.
(5) In a method of surface-treating particles with a derivative of amino aced such as lysine or glutamic acid in an aqueous dispersion solution, as disclosed in EU Patent No. 139481, the cosmetic particles thus prepared have good affinity to the skin, hence good adhesion but are easily removed with water due to low water resistance.
As described above, amino acids and their derivatives have been conventionally used to provide affinity to the skin for the pigment of color cosmetics. Examples of the amino acid include N-acylated derivatives of L-lysine (i.e., basic amino acids) and of glutamic acid (i.e., acidic amino acids). Such an amino acid treated pigment is superior in adherence to the skin to other pigments but easily removed with water. Thus, the amino acid treated pigment is hard to mix in a large amount with color cosmetics that require good durability.
On the other hand, there is a case where an inorganic pigment is treated with a mixture of perfluoroalkyl phosphate as a fluoride component and lauroyl lysine as an amino acid component. Such a composite pigment improves deterioration of adhesion to the skin but requires a large amount of coating that increases entirely the content of the two processing agents in excess of 5% of the pigment. Coating with an excess of such processing agents makes the coating inhomogeneous to entirely impair the cosmetic effect and results in a compression-molded formulation excessively hard. Thus, it becomes difficult to control the pay-off amount of the cosmetic particles by means of a cosmetic tool such as powder puff or tip.
Alternatively, EU Patent No. 725056 discloses a method for preparing fluoroalkyloxycarbonyl lysine chemically synthesized from a fluoride group as a fluoride component and an amino acid, and a method for surface-treating an inorganic pigment.
A composite surface treatment method using fluorides and an inorganic pigment surface treatment method using a novel surface treatment agent effectively improve the disadvantage of the surface treatment method using fluorides, i.e., deterioration of affinity to the skin. However, the methods are inapplicable to a cosmetic requiring usability, since the fluoride derivative as a pigment treatment agent is not excellent in the lubricating ability. Furthermore, the cosmetic prepared by the method is a solid containing the treatment agent having a melting point of higher than 200.degree. C. and thereby is inferior in the usability to the liquid-state cosmetic surface-treated with silicon that has a good lubricating ability at a room temperature.
The keratin layer constituting the outermost layer of the skin is a layer in direct contact with the color cosmetic particles. It is known that the keratin layer is a slightly acidic and negatively charged. However, an inorganic extender pigments such as talc, mica, sericite and kaoline and a pigment surface-treated with silicon, fluoride and metallic soap, as conventionally applied to the cosmetic particles, are negatively charged or take no surface charges and thus difficult to adhere to the skin in an electrostatic manner. And, the adhesion of these color cosmetics primarily depends on the viscosity and the liquidity of binding oil such as mineral oil, fatty acid ester and dimethyl polysiloxane. The binding oil is absorbed in the skin over time after taking a make-up and has a deterioration of binding performance after an elapse of time, so that the cosmetic particles aggregating and coming undone from the skin are easily removed. Therefore, adhesion of the pigment by the binding oil adversely results in deterioration of the affinity of the cosmetic to the skin due to a lack in electrostatic bonding, thus inefficiently providing an effect of the surface treatment agent.